1. Field of the Invention
The present invention relates to a gear change controller for an automatic transmission.
2. Description of the Prior Art
A gear change controller for an automatic transmission is described for example in Japanese Patent Publication No.3-22328.
A conventional gear change controller for an automatic transmission performs gear change by comparing a vehicle speed V and throttle opening T input to a computer by a vehicle speed sensor and throttle opening sensor, with a kinked line (gear change-over line) expressing "vehicle speed/throttle opening" characteristics. Such kinked lines are prepared for up-shifting and down-shifting respectively as shown in FIG. 5. Numbers in FIG. 5 correspond to each gear positions. Thus, for instance, the kinked line A is used when up-shifting from the second gear position to the third gear position is determined, and the kinked line B is used when down-shifting from the third gear position to the second gear position is determined.
More specifically, when changing gear position, an interpolation value Vp' is determined on the kinked line expressing "vehicle speed/throttle opening" characteristics based on the present throttle opening Tp, the interpolation value Vp' is then compared with the present vehicle speed V, and the required gear change is then determined from their relative magnitudes.
The interpolation value Vp' is calculated by reading a slope ai of the linear portion to which the throttle opening Tp corresponds and coordinates (Ti, Vi) of the lower end of this linear portion, and performing the following computation. EQU Vp'=ai(Tp-Ti)+Vi 1)
where ai is the slope of the corresponding linear portion.
If the interpolation value Vp' is larger than present vehicle speed Vp, the gear selection actuator is controlled so as to perform a gear change-over.
Hence, in above-described gear change controller, when determining a required gear change, there is no need to perform a division calculation in order to obtain the interpolation value.
The calculation is therefore processed in a short time and with a small number of steps.
In the above-described prior art, the kinked line (gear change-over line) expressing "vehicle speed/throttle opening" characteristics was stored in terms of the slope ai of the elemental linear portions of the line and the coordinates (Ti, Vi) of the lower ends of these portions.
Since data is expressed as integers in a memory of the computer, the slopes of these linear portions therefore also had to be expressed as integers. However, not many slopes can be expressed as integers, so that there was not much freedom in setting the gear change-over line.